High Cardiorespiratory Fitness
Research: An incentive for a healthier life.
Lee, D., et al. 2010. Mortality trends in the general population: The importance of cardiorespiratory fitness. Journal of Psychopharmacology, 24 (11), 27–35.
Recently a task force of scientists selected by the American Heart Association (AHA) introduced the 2020 U.S. “Impact Goals” for cardiovascular health and disease reduction (Lloyd-Jones et al. 2010). The goals are as follows: “By 2020, to improve the cardiovascular health of all Americans by 20% while reducing deaths from cardiovascular diseases and stroke by 20%.”
Confronted with how to define and measure ideal cardiovascular health, the task force identified four health behaviors and three health factors:
4 Health Behaviors
- body mass index < 25 kg/m2
- physical activity (150 minutes per week of moderate-intensity exercise or 75 minutes per week of vigorous-intensity exercise, or a combination of these two)
- consumption of a diet that promotes cardiovascular health (emphasis on a low glycemic load, high fiber, high marine omega-3 fatty acids, high polyunsaturated to saturated fat ratio, and low trans fat content)
3 Health Factors
- total cholesterol < 200 milligrams per deciliter (mg/dL)
- fasting blood glucose < 100 mg/dL
- blood pressure < 120/80 mm Hg
The new Impact Goals document declares that as men and women raise their levels of physical activity by increasing the intensity, frequency and/or duration of that activity, they experience much healthier lives. Moreover, coinciding with the release of the new AHA goals, new evidence suggests that low cardiorespiratory fitness (CRF) is as strong a predictor of cardiovascular disease (CVD) and other health causes of mortality (referred to as all-cause mortality) as are well-established risk factors such as smoking, obesity, hypertension and diabetes (Lee et al. 2010).
Cardiorespiratory fitness can be defined as the ability of the respiratory, circulatory and muscular systems to consume, distribute and utilize oxygen during continuous physical activity (Lee et al. 2010). CRF is measured in milliliters of oxygen per kilogram of body weight per minute (ml O2/kg/min). This research column will review the new research examining the importance of CRF for CVD risk reduction.
Lee et al. (2010) summarize several research studies that have compellingly demonstrated that moderate to high levels of CRF are associated with a reduced risk of CVD. In one paper—a recent and original meta-analysis of studies on CRF and mortality and on CRF and coronary heart disease (CHD) and CVD events—Kodama et al. (2009) review 33 investigations into these topics (all-cause mortality: 102,980 participants and 6,910 cases; CHD/CVD events: 84,323 participants and 4,485 cases). Based on this analysis, Kodama and colleagues report that each 1-MET increase in CRF is associated with risk reductions of 13% and 15% for all-cause mortality and CHD/CVD events, respectively (see the sidebar “5 Questions and Answers About CRF” for more on the MET).
Persons with low CRF have a higher risk of all causes of mortality and CHD/CVD events than persons with moderate to high levels of CRF, conclude Kodama and colleagues. They add that the CHD/CVD risk reduction observed with higher CRF levels is present regardless of a person’s age, sex, body mass index and smoking status.
With the association between low levels of CRF and CVD risk well established, a meaningful question to ask is whether improvements in CRF will also result in positive changes in CVD risk.
Erikssen et al. (1998) followed 2,014 healthy men (aged 40–60 at baseline) for a total of 22 years. The researchers report that improvements in CRF within a 7-year period early in the study were associated with significant risk reduction from all causes of mortality during the follow-up.
Given the research, you can confidently inform your clients that by improving their fitness level they are actually developing healthier lives and reducing disease risk. Lee et al. (2010) cite research showing that individuals who improved their CRF from low levels to moderate and/or high levels meaningfully reduced their risk of CVD. Other causes of mortality also decreased. Erikssen and colleagues emphasize that even small improvements in CRF resulted in significant CVD risk reductions, which is a very encouraging incentive to share with clients.
Lee et al. (2010) indicate that there are several mechanisms to explain how improved CRF reduces the risk for CVD and all causes of mortality (see Figure 1). Among the key mechanisms, the relationship of CRF to insulin resistance (a condition in which cells of the body become resistant to the effects of insulin, impairing the cell’s ability to take up and use glucose) comes to the forefront. Higher levels of CRF improve insulin sensitivity, thus improving the cell’s ability to use glucose as a fuel and helping to prevent or manage type 2 diabetes.
Second, Lee and colleagues recap data showing that persons with higher CRF have a lower risk of all variables in metabolic syndrome (waist circumference, triglycerides, HDL-cholesterol, blood pressure, fasting blood glucose). Persons with metabolic syndrome are very likely to develop CVD and diabetes.
Recent studies show that CRF is an excellent measure of several bodily functions highly associated with CVD and all causes of mortality. According to the data, one of the most important strategies that personal trainers can incorporate into their clients’ training is a goal to increase CRF, as it is likely to bring substantial health benefits. Get moving and keep going!
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- What is a MET and how is it used?
A MET is a standardized unit of measurement for expressing exercise workload. The estimated energy expenditure cost at rest is 1 MET, which is equal to 3.5 ml O2/kg/min. In some exercise training situations, such as cardiac rehabilitation and research studies, exercise professionals design clients’ workout intensities using METs.
- Is there a gender difference for maximal aerobic capacity? Yes. On average, maximal aerobic capacity in women is roughly 2 METs lower than it is in men, owing to women’s smaller muscle mass, lower hemoglobin and blood volume, and smaller stroke volume (Lee et al. 2010).
- How does obesity affect CRF? Wang et al. (2010) have shown that regardless of race, gender or ethnicity, people who are obese have significantly lower CRF levels (~15% lower) than nonobese adults.
- What are the main limitations to CRF? The main limitations to CRF are often referred to as “central and peripheral factors.” Central factors include oxygen delivery to muscles during endurance exercise; delivery may be limited by pulmonary diffusion (exchange of oxygen and carbon dioxide between the lungs and the blood), maximal cardiac output (the product of heart rate and stroke volume) and the blood’s oxygen-carrying capacity. Peripheral factors refer to the ability of exercising muscles to extract and use oxygen that has been transported by the cardiorespiratory system.
- What is the best way to improve CRF? For greater improvements in CRF, the American College of Sports Medicine (ACSM) advocates 3–5 days per week of cardiovascular exercise at 64%–94% of maximum heart rate (Whaley 2005). A duration of 20–60 minutes is encouraged for continuous training and for interval training programs. Progressive increases in intensity and duration must be incorporated into the exercise program to achieve higher levels of CRF, suggests ACSM.
Kodama, S., et al. 2009. Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women; a meta-analysis. Journal of the American Medical Association, 301 (19), 2024–35.
Lloyd-Jones, D.M., et al. 2010. Defining and setting national goals for cardiovascular health promotion and disease reduction: The American Heart Association’s strategic Impact Goal through 2020 and beyond. Circulation, 121, 586-613. http://circ.ahajournals.org/cgi/content/full/121/4/586.
Wang, C-Y., et al. 2010. Cardiorespiratory fitness levels among US adults 20-49 years of age: Findings from the 1999-2004 National Health and Nutrition Examination Survey. American Journal of Epidemiology, 171 (4), 426–35.
Whaley, M.H. (Ed.) 2005. ACSM’s Guidelines for Exercise Testing and Prescription (7th ed.). Philadelphia: Lippincott Williams & Wilkins.
© 2011 by IDEA Health & Fitness Inc. All rights reserved. Reproduction without permission is strictly prohibited.
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